(a) Field of the Invention
The present invention relates to a filtering circuit having the behaviour of a low-pass R-C filter but capable of having a large time constant.
(b) Description of Prior Art
Various types of circuits are known for sampling or monitoring a signal. For example, averager circuits are known for this purpose, but the disadvantages of these is that they give an average result at the end of each integration period, they are expensive to fabricate, have a very limiting characteristic, they cannot utilize small power supplies as they have a high power consumption and are bulky to package. Also, this type of sampling does not provide an immediate updated output.
When considering an RC filter circuit to solve the low frequency problem of averagers, it also has limitations at such low frequencies and cannot be used to filter with large time constant, that is to say, hours or days. With RC circuits, this is related to the problem of capacitance leakage and also the component parts of an RC filter design are considered large in size when compared to component packages such as those nowadays provided when a circuit is etched on a single chip.